Aziridinium ions have been utilized as reactive intermediates in asymmetric synthesis of pharmaceuticals, and other complex natural products. In addition, aziridinium ions are involved in anticancer activity of nitrogen mustards and anticancer drugs such as chlorambucil (CMB), mechlorethamine, and phosphamide mustard. The reaction of aziridinium ion intermediates derived from the mustards with guanine residues in DNA to form interstrand cross-link has been found to produce the biological activity. Although aziridinium ions possess great potential as building blocks for preparation of biologically active molecules, the reactivity and synthetic applications of aziridinium ions has not been systematically investigated. This is in part due to difficulties in isolation and characterization of the strained three-membered rings and the lack of general and efficient methods for synthesis of optically active aziridinium ions with functionalities. Aziridinium salts are amphiphilic species that can possess both nucleophilic and electrophilic components. The electrophilic carbons in the aziridinium salts are expected to react with nucleophiles under mild conditions, and the nucelophilic N-substituents, C-substitutents, or counteranions in the salts can also attack the electrophilic carbon present in the aziridinium ion in intramolecular nucleophilic reactions. While the other three-membered aziridines and epoxides have numerous applications in organic synthesis of important drugs, applications of aziridinium ion chemistry to drug synthesis remains an under-explored area.